1. Field of the Invention
The present invention relates to an apparatus for measuring an internal quality of such an object as the greengrocery (fruits and vegetables) on a nondestructive basis.
2. Related Background Art
An example of the conventional apparatus for measuring the internal quality of the fruits or vegetables on a non-destructive basis was a device disclosed, for example, in Japanese Patent Application Laid-Open No. 6-213804. The conventional apparatus will be described below referring to FIG. 37 and FIG. 38.
In the apparatus illustrated in FIG. 37, light 854 is projected from lamp 853 toward an object to be inspected (inspected object) 852 such as a mandarin, an orange, an apple, or the like mounted on belt conveyor 850 and a spectroscope 858 receives light 856 having been transmitted by and emitted from the inspected object 852. The spectroscope 858 measures an absorption spectrum of the transmitted light 824 and the internal quality of the inspected object can be determined based on the absorption spectrum.
With this apparatus, variations occurred in measured values as a plurality of inspected objects 852 on the conveyor 850 were measured continuously. This is conceivably caused by change of a base line (which is a value as a reference of measurement) of the measured values of the spectroscope with a lapse of measurement time. This change mainly results from changes of the spectroscope and the apparatus itself and from change in ambient circumstances.
Another device for measuring the internal quality of the fruits or vegetables such as melons or the like on a non-destructive basis was, for example, a device disclosed in Japanese Patent Application Laid-Open No. 6-288903. The conventional device will be described below referring to FIG. 39.
In this device, near-infrared light is projected from lamps 876 toward the inspected object 874 such as a melon or the like mounted on a shield basket 872 on belt conveyor 870 and the spectroscope 880 receives light having been transmitted by and emitted from the inspected object 874 through optical fiber 878. The spectroscope 880 measures an absorption spectrum of the transmitted light and the internal quality of the inspected object 880 can be determined based on this absorption spectrum.
With this device, variations occurred in measured values as a plurality of inspected objects 874 each mounted on a plurality of shield baskets 872 were measured continuously. This is conceivably caused by change of the base line (which is a value as a reference or standard of measurement) of the measured values of the spectroscope 880 with a lapse of measurement time. This change mainly results from changes in the spectroscope 880 and in the ambient circumstances.
With the conventional apparatus, however, adjustment (i.e., calibration) of the base line changing with a lapse of measurement time was carried out only at the start of measurement, so that the variations occurred in the measured values with progress of measurement with a lapse of time.
On the other hand, for carrying out the calibration in the middle of the measurement, the conveyor line had to be stopped on every occasion of calibration and the measurement also had to be suspended. Therefore, the measurement time was lengthened for execution of the calibration.
In the apparatus illustrated in FIG. 38, light 862 reflected by half mirror 860 is projected toward the inspected object 852 mounted on the belt conveyor 850 and the spectroscope 858 receives light 864 having been reflected by the inspected object 852 and having passed through the half mirror 860, whereby the internal quality of the inspected object 852 can be determined as in the case of the apparatus of FIG. 37. In this device the spectroscope 858 and reference reflecting plate 866 for calibration are opposed to each other on either side of the belt conveyor 850 and with the reflected light from this reflecting plate 866 the calibration can be carried out at a position where the inspected object is absent on the conveyor 850.
The calibration according to this method, however, cannot be applied to the device of FIG. 37 for measuring the light having been transmitted by the inspected object.
An object of the present invention is, therefore, to provide a device for measuring an internal quality of a fruit or vegetable with light having been transmitted by the inspected object, the device being arranged in such structure that the calibration of the device can be carried out without interruption of the measurement, so as to eliminate the change of the base line, whereby the internal quality of the fruit or vegetable can be measured accurately.
On the other hand, in the measurement of the internal quality by spectral analysis as described above, it is common practice to project the light from the light source such as a halogen lamp or the like toward the fruit or vegetable, divide the transmitted light through the fruit or vegetable into a plurality of channels having different wavelengths, convert the intensity of the transmitted light in each channel to current, measure the current to detect an absorption spectrum of the fruit or vegetable, and determine a sugariness or the like of the fruit or vegetable, based thereon. In such measurement, it is inevitable to suffer fluctuations of the light source lamp, specifically, temporal change and deterioration of spectral characteristics (color temperature), and fluctuations due to environmental change of ambient temperature or the like on one hand and it is also inevitable to experience fluctuations and the like due to temporal change or environmental change of the measurement system on the other hand, which results in causing errors in the measurement.
In order to avoid it, in the case of such measurement, the calibration of the device is carried out at intervals of a certain time. The calibration is carried out by measuring the quantity of the transmitted light through a predetermined calibration body instead of the fruit or vegetable being an object originally intended to be inspected. A typical calibration method is as follows. In each wavelength channel, a measurement transmittance T is calculated according to the following equation to effect the calibration: EQU T=I.sub.s /I.sub.r
where I.sub.r is the intensity of the transmitted light (more exactly, intensity of current converted therefrom) through the calibration body and I.sub.s is the intensity of the transmitted light (more exactly, intensity of current converted therefrom) of the fruit or vegetable to be inspected. Namely, a value of transmittance of an inspected object is calibrated by taking a ratio thereof to the transmittance of the calibration body, thereby canceling the change of the transmitted light due to the variations of the light source and the measurement system.
For more accurate measurement, the transmittance is also sometimes computed according to the following equation: EQU T=(I.sub.s -D)/(I.sub.r -D)
where D is dark current of the measurement system when the input into the spectroscope is zero.
The calibration body used in such calibration is normally an object with flat absorption characteristics such as an ND filter (neutral density filter) or the like. The reason why the light from the light source is not monitored directly but is monitored through the ND filter on the occasion of the calibration is that the intensity of light needs to be of a light intensity level close to the intensity of the transmitted light through actual inspected bodies in order to make the calibration accurate. It is, therefore, common practice to select the transmittance of the ND filter for calibration so that the quantity of the transmitted light therethrough is within a predetermined range with respect to the quantity of the transmitted light through the actual inspected bodies.
As described above, the calibration is carried out using the calibration body such as the ND filter or the like against the various variations of the measuring device. However, the fruits or vegetables being actual inspected objects have specific light absorption characteristics, because the principal component thereof is water; whereas the ND filter has the flat absorption characteristics. Because of this great difference in the absorption characteristics, the flat absorption characteristics of the ND filter cannot follow the largely changing absorption characteristics of the fruits or vegetables, so that the intensity of the transmitted light through the calibration body and the intensity of the transmitted light through the inspected objects become heavily different from each other, depending upon the wavelengths, which poses a problem of failing to effect the calibration with high accuracy.
There are problematic variations during the measurement by infrared spectral analysis, not only on the device side but also on the object side.
Specifically, the principle of the measurement of the internal quality such as the sugariness, acidity, or the like of the fruits or vegetables by the infrared spectral analysis is based on the fact that absorption occurs at specific wavelengths in the spectrum of transmitted light because of various groups (for example, functional groups such as O--H, C--H, and so on) of components in the fruits or vegetables being the inspected objects. The absorption spectra of the fruits or vegetables vary depending upon environmental changes of the temperature or the like and variations also occur in peak wavelengths of absorption by the groups. This results in introducing errors in the measurement of the internal quality by the spectral analysis. This is significant, particularly, in the measurement of the acidity of a low-content acid or the like. The ND filter does not have a variable property of the absorption characteristics against the environmental change, and thus the ND filter is inadequate as a calibration body in this aspect, too.
In the conventional measuring apparatus for measuring the internal quality of the fruits or vegetables by spectral analysis, the position where the calibration body is measured is different from the position where the inspected object is measured in the apparatus, which is a reason why variations of their absorption spectra measured are not synchronous.
The present invention provides a correction method which solves the above problem.
In addition, values of such internal qualities as the sugariness, acidity, grade of maturity, and so on of the fruits or vegetables differ depending upon locations in the fruits or vegetables. It is thus desirable to project the light toward the central part of the fruit or vegetable, in the apparatus arranged to project the light toward the fruit or vegetable and measure the internal quality thereof with the light transmitted thereby.
In the conventional example, however, the height of the projection light source was fixed, and, therefore, if the sizes of the fruits or vegetables being the inspected objects were different, irradiation positions were different between large inspected objects and small inspected objects. Namely, the light was projected toward the central part of inspected object with the small inspected objects, whereas the light was projected to the lower part of inspected object with the large inspected objects. It was not able to be mentioned that each of the inspected objects was measured under the same conditions.
On the other hand, the measuring device of this type is arranged to measure the internal quality of the fruit or vegetable by the absorption spectrum of the light having been transmitted by the fruit or vegetable, and it is desirable that the absorption spectrum have the intensity enough to implement accurate measurement.
However, the quantity of the light transmitted by the fruits or vegetables under irradiation of the light at constant quantity is sometimes very small, depending upon kinds of the fruits or vegetables. In that case the measurement becomes hard. In general, melons, watermelons, etc. transmit the light in small quantity while oranges etc. transmit the light in large quantity. For measuring the internal quality of the fruits or vegetables with the small quantity of transmitted light, the difference is unlikely to appear among intensities of the absorption spectra of the respective inspected objects and it is thus difficult to implement the measurement by the absorption spectra.
An object of the present invention is, therefore, to provide a measuring device for measuring an internal quality of a fruit or vegetable on a non-destructive basis while projecting light toward the fruit or vegetable, the measuring device being arranged to be capable of radiating the light to the vicinity of the equator part (an intersecting line between a horizontal plane including the central part of the inspected object and being parallel to the ground and the surface of the inspected object) of the inspected object, irrespective of the size of the inspected object and to be capable of changing the quantity of the projected light toward the fruit or vegetable according to a kind of the fruit or vegetable.
In many non-destructive measuring devices of fruits or vegetables for measuring the internal quality such as the sugariness, acidity, or the like of the fruits or vegetables by projecting the light such as the near-infrared light or the like toward the fruit or vegetable and measuring the absorption spectrum of the transmitted light, a plurality of fruits or vegetables as inspected objects are mounted on a conveying system such as a belt conveyor or the like and the measurement is carried out successively for the plurality of inspected objects under movement.
Specifically, located at a certain position in a conveyance path of the conveyor is a measurement unit comprised of a light projecting device for projecting the light toward the inspected object and a sensor for receiving the transmitted light from the inspected object to measure the absorption spectrum thereof, and the measurement is carried out when each inspected object passes the measuring position. Then the sugariness, acidity, or the like of each fruit or vegetable being an inspected object is computed based on the absorption spectrum obtained.
In this measuring device, it is desirable to implement the measurement at the center position of the fruit or vegetable being the inspected object in order to realize the measurement with less errors. Among the devices of this type, devices in such structure that buckets for accommodating individual inspected objects are provided on the conveyor and that the inspected objects are mounted on the respective buckets, permit easy determination of the correct measurement timing, i.e., easy determination of the timing when the inspected object passes the measuring position, because the positions of the inspected objects on the conveyor are preliminarily determined at the predetermined positions. On the other hand, in the case of the fruits or vegetables such as oranges or the like where a large amount of inspected objects need to be measured, a way of measuring them while such fruits or vegetables being the inspected objects are supplied and mounted at random on the flat belt conveyor by automatic supply means or the like is more useful in terms of measurement efficiency. In cases where the inspected objects are placed at random on the conveyor, it is, however, necessary to substantiate some means for carrying out the measurement at the correct measurement position, i.e., at the time when the center of the inspected object passes the measuring position. The present invention provides a method and an apparatus that enable such measurement.
When the fruits or vegetables such as oranges or the like are placed at random on the flat conveyor as described above, the inspected objects could rotate to move on the conveyor in some cases because of the property of the shape of the fruits or vegetables close to the sphere. In such cases there arises a problem that it is not clear whether an inspected object leaving the conveyor was measured at the normal position. The present invention also solves this problem.
Further, the apparatus of this type normally has moving means such as a belt conveyor or the like for continuously moving a plurality of fruits or vegetables along a conveyance path, a light source disposed at a predetermined position in a conveyance path established by the moving means and arranged to project light toward the fruit or vegetable on the moving means, and a light receiving sensor for receiving light travelling through the fruit or vegetable, as main components.
The devices conventionally known are generally classified as follows.
1) devices of a type in which the light receiving sensor is located at a position in a direction approximately equal to the direction of the light projected from the light source toward the fruit or vegetable of the inspected object and in which the measurement is carried out by receiving scattered and reflected light which penetrates several millimeters into the surface of the fruit or vegetable (this type will be referred to as a reflection type); PA1 2) devices of a type in which the light from the light source (normally, one lamp) is projected from the side to the fruit or vegetable of the inspected object and in which the light receiving sensor is located at a position where it is opposed to the light source with the fruit or vegetable in between so as to receive the transmitted light (this type will be referred to as an opposite reception type); PA1 3) devices of a type in which the light source (many lamps in many cases) is located on the side of the fruit or vegetable of the inspected object mounted on the shield carrier (or basket), the light is projected from the side, the transmitted light scattered inside the fruit or vegetable and emitted from the bottom is guided from the bottom through a hole bored in the carrier, and the transmitted light is received by the light receiving sensor disposed below the fruit or vegetable in a direction perpendicular to the direction of the projected light (this type will be referred to as a lower reception type).
Among these types, the reflection type devices can be used only for limited kinds of fruits or vegetables suitable for the measurement, because they can obtain only information of the internal quality of the region from the surface of the inspected fruit up to the depth of about several millimeters. In order to extract the information of the internal quality of deep part of the fruits or vegetables, it is necessary to select one of the devices using the transmission methods of 2) and 3) described above.
The devices using the conventional transmission methods described above, however, had the following problems.
In the case of the devices of the opposite reception type, since the measuring light passes through the lateral diameter of the fruits or vegetables, optical path lengths are considerably long. When the inspected object is one resistant to the transmission of light, such as an apple, a peach, or the like, the light having been transmitted and emitted by the inspected object is very weak, thus posing a problem of failing to capture a signal. Particularly, there also arises a problem that the light is more unlikely to pass in the long-wavelength region including the spectral absorption important for the measurement of the internal quality of the fruits or vegetables. The quantity of the transmitted light can possibly be increased by increasing the quantity of the projected light, but it is difficult to increase the quantity of the projected light in the case of the opposite reception type, because the light projection system is normally limited to one lamp because of the structure.
In contrast with it, in the case of the devices of the lower reception type, since the light can be projected from a plurality of directions on the side of the inspected fruit or vegetable, the quantity of the projected light can be increased by employing a multiple lamp method with plural light sources. Since the transmitted light is guided downward, optical path lengths inside the fruit or vegetable can be shorter than in the case of the opposite reception type. Therefore, this type has no problem in terms of the quantity of the transmitted light and effective measurement can also be carried out for fruits or vegetables unsuitable for the opposite reception type.
In the case of the lower reception type, however, in order to guide the detected light out of the bottom, it is necessary to use the bored carriers or to bore holes in the conveyor, which poses a problem that the structure of the conveying system becomes complicated. Since the inspected fruits or vegetables have to be mounted as positioned at the positions of the holes of the conveyor or as positioned on the carriers, there arises a problem that a supply mechanism for mounting the fruits or vegetables has to be provided or that an operator has to place the fruits or vegetables one by one on the occasion of the measurement. In either case the measurement efficiency of the apparatus is lowered and it is a significant problem for the fruit or vegetable internal quality evaluating apparatus that often needs to continuously measure a lot of inspected objects.
A further problem is that assembling of the apparatus and labor of maintenance thereof become complicated, because the light receiving sensor has to be set below the belt conveyor, i.e., within a loop of the belt conveyor.